Head for a two piece articulated piston

ABSTRACT

A method for the manufacture of a cooled piston head in which the upper and lower portions of the piston head are made separately a metal plate is placed on the lower side of the upper portion; then the upper portion incorporating the metal plate is joined to the lower portion by friction welding. The metal plate is provided with a central hole for the passage of cooling oil onto the undercrown, and means of communication with a closed cooling chamber defined by a circumferential groove on the head upper portion and the peripheral outer surface of the metal plate.

RELATED APPLICATION

This application is a division of application Ser. No. 07/688,147 filedApr. 19, 1991 now U.S. Pat. No. 5,230,148.

BACKGROUND OF THE INVENTION

The present invention relates to a method for the manufacture of acooled piston for use in internal combustion engines. Particularly, theinvention deals with a method to manufacture the upper part, or head ofa two-piece, or articulated, piston provided with improved coolingmeans.

The main components, i.e., the head and the skirt, of articulatedpistons are independent members. The head, composed of the top and thepin boss portions, is generally made of forged or cast steel, and theskirt is made of a lighter material, generally aluminum or an aluminumalloy. This type of piston is being adopted for diesel engines,especially last generation diesel engines, where combustion pressuresand temperatures in the engine are very high. Owing to these conditions,which are extremely adverse to the piston head, it has been a commonpractice to provide the piston crown with a cooling chamber for thecirculation of oil to remove part of the heat from at least two regionsvery susceptible to the influence of elevated temperatures: the ringband and the combustion bowl rim.

One traditional cooling chamber construction consists of providing acircumferential groove at the piston crown between the combustion bowland the ring band, and a circumferential trough, or tray, on the skirtupper portion, whereby with the piston assembled the groove and the traydefine a semi-open cooling chamber for the circulation of cooling oil.

While suitable for most applications, this type of chamber is notentirely satisfactory when a higher cooling efficiency is required. Onedisadvantage is a poor cooling of the undercrown, i.e., the regionunderneath the combustion bowl, which is not reached by the chambercooling action. Another disadvantage arises from the construction itselfof the semi-open chamber; part of the cooling oil flows from the tray onthe skirt upper portion thereby reducing the quantity of oil in thechamber and, accordingly decreasing the cooling efficiency on the ringband and combustion bowl wall regions.

OBJECTS OF THE INVENTION

With a view to solving this problem, the present invention has theobjective of providing a method to manufacture an articulated pistonhead by which there is provided effective cooling means for all of thepiston head portions most subjected to high temperatures, namely thering band, the combustion bowl wall and the undercrown.

BRIEF DESCRIPTION OF THE INVENTION

According to the method for the manufacture of an articulated pistonhead of the present invention, the two portions comprising the pistonhead, i.e., the top portion and the pin boss portion, are madeseparately, a cooling oil tray being installed on the top lower portionand thereafter the top portion incorporating the cooling oil tray beingjoined to the pin boss portion.

It is a further object of the present invention to produce anarticulated piston head provided with a closed cooling chamberincorporated to the head according to the method of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be hereinafter described in greater detail withreference to the accompanying drawings where:

FIG. 1 is a longitudinal sectional view of a blank from which the upperportion of the piston head of the invention will be made;

FIG. 2 is a longitudinal sectional view of a blank from which the lowerportion of the piston head of the invention will be made;

FIG. 3 is a longitudinal sectional view of the upper portion of thepiston head of the present invention made from the blank shown on FIG.1;

FIG. 4 is a plan view of the tray which defines the bottom of thecooling chamber of the piston of the invention;

FIG. 4a is a cross-sectional view of the tray depicted in FIG. 4;

FIG. 5 is a longitudinal section view of the upper portion of the pistonhead with the tray of FIG. 4 provided on the bottom of the upper portionaccording to the invention;

FIG. 6 is a longitudinal sectional view of the lower portion, or pinboss portion, of the piston head of the invention made from the blank ofFIG. 2;

FIG. 7 is a longitudinal section view of the piston head of theinvention showing the upper and lower portions joined together; and

FIG. 8 is a longitudinal section view of the piston head of theinvention showing the upper and lower portions machined to their finaldimensions.

DETAILED DESCRIPTION OF THE INVENTION

According to a preferred d embodiment of the invention, there isprovided a blank 1, preferably of steel and obtained by forging,continuous casting or sintering. The blank 1 is preferably a cylindricalbody having a diameter as close as possible to that of the finishedpart, whereby it is possible to reduce machining operations which isbeneficial to the final cost. The blank 1 is subjected to a first seriesof machining operations for the provision of an upper combustion bowl 3,a lower circumferential groove 4 and a recess underneath the combustionbowl 3, so as to define a plurality of semiperipheral oblong-shaped webs5 angularly spaced apart from each other (FIG. 3). Thereafter, asubstantially circular plate 6, preferably of steel, is provided with acenter hole 6e, a plurality of slots 6c spaced from each other byregions 6d, defining an outer peripheral surface 6a and an innerperipheral surface 6b, as shown in FIG. 4 and 4a. In the subsequentoperation, the plate 6 is placed on the lower part of portion 1 byfitting the oblong shaped webs 5 of upper portion 1 into the slots 6c ofplate 6. In this manner, the outer peripheral surface 6a is positionedsuch as to close the circumferential groove 4 defining with said groove4 a closed chamber 10 (FIG. 5).

Thereafter, there is provided a blank 2, which may be of the samematerial of blank 1 and obtained by the same process, preferably havinga cross section substantially similar to the shape of the pin bosses intheir final form. Blank 2 is subjected to the machining to provide acircumferential recess at one of its ends and a narrowing of itsdiameter around the recess thereby defining a circumferential web 2a.The blank 2 is then joined to blank 1 by means of the juxtaposition ofthe top face of the circumferential web 2a of blank 2 with the lower endof webs 5, the joining being carried out by welding, preferably byfriction welding. The friction welding method is preferred for itperforms the joining without causing the melting of the materials to bewelded, thus preventing the occurrence of porosities which could impairthe bonding strength. Upon the completion of the welding, plate 6 isfirmly held in the piston head and the outer peripheral surface 6acloses the groove 4 to define a closed chamber 10 for the cooling oil(FIG. 7). Finally, the head comprising top 1 and pin bosses 2 andincorporating plate 6 is subjected to the final machining operations forprovision of the pin bosses 9, the pin holes 8 and the ring grooves 7.

The supply of the cooling oil to the chamber is made by means of anozzle (not shown), the oil is injected through the central hole 6e ofplate 6 and hits the undercrown, thus removing part of the heatgenerated in that region. Thereafter, a portion of the oil thus suppliedreturns to the engine crankcase through the same central hole 6e and theremaining oil flows toward chamber 10 through the regions 6d of plate 6.With the reciprocating motion of the piston, the oil confined in thechamber 10 is subjected to a cocktailshaker-like effect, therebyremoving part of the heat from the combustion bowl wall and the ringregion. The supply of oil is provided in a continuous cycle, thus atleast part of the oil in the chamber is always fresh, which ensures anefficient cooling and the maintenance of optimum temperature conditionson the several portions of the piston head.

What is claimed is:
 1. A cooled piston head for a piston of thetwo-piece articulated type for use in internal combustion engines,comprising:an upper portion with a lower face provided with acircumferential groove, a central recess and a plurality of downwardlyextending sectors of a circular web between said circumferential grooveand said central recess and a lateral outer face; a circular metal platehaving a plurality of slots in a circumferential arrangement each toaccept a said sector of the circular web, said circular metal platebeing seated relative to the lower face of said upper portion in to havethe sectors of the circular web fitted into the slots of the circularmetal plate, the portions of the metal plate between the slots spacedfrom said upper portion lower face and connecting a peripheral outersurface defining, with the circumferential groove of the upper portion aclosed cooling chamber communication with the spaces between said websectors; and a lower portion having an upper peripheral web welded tosaid circular web sectors of the upper portion, said lower portionhaving pin bosses and pin holes.
 2. The piston head of claim 1, whereinsaid circular metal plate is provided has a central portion spaced formsaid upper portion lower face with a hole through which a lubricant isadmitted and travels to said cooling chamber through the spaces betweensaid sectors.
 3. The piston head of claim 1 wherein the lateral outerface of said upper portion has at least one ring groove thereon.
 4. Thepiston head of claim 1 wherein an upper face of said upper portion has arecess overlying the central recess on the lower face of said upperportion.
 5. The piston head of claim 1 wherein said metal platecircumferential portion is substantially flat and extends to the lateralwall of said upper portion.
 6. The piston head of claim 2 wherein saidcentral portion of said metal plate faces the central recess on thelower face of said upper portion.